When electronic apparatus, e.g. projectors, are operating, heat is increasingly generated. For example, when a projector is in use, the projecting light source as well as other electronic components inside the projector generate a great deal of heat. In general, a heat dissipation system is implemented to dissipate the heat and to prevent electronic apparatus from over-heat shorting their lives. When the inner temperature of the electronic apparatus exceeds the designed operating temperature, the electronic apparatus fails. Among many dissipation techniques, one is to utilize the air to cool the device. In this case, a fan is often configured to guide a cooling airflow in and out of the casing taking away the heat.
As shown in FIG. 1, a conventional heat dissipation system is illustrated. An electronic device having a casing 10 includes an inlet 132 and an outlet 134. A fan 122 is disposed close to the inlet 132 of the casing 10 for guiding airflow into the casing 10 through the inlet 132. A fan 124 is disposed close to the outlet 134 for guiding the airflow out of the casing 10 through the outlet 134. The faster the fans 122 and 124 rotate, the better the heat dissipation. However, the noise accordingly escalates. To reduce the unnecessary noise, the fans 122 and 124 rotate at a less speed providing sufficient heat dissipation when the inner temperature is lower. When the inner temperature increases, the fans 122 and 124 rotate faster so as to provide more effective heat dissipation. The relation between the temperature and the speed of the fan is controlled by the microprocessor 102. Accordingly, a thermal sensor 104 is disposed near the inlet 132 to detect the corresponding temperature, and a signal representing the temperature is then transmitted from the thermal sensor 104 to the microprocessor 102 through a signal line 112. Through signal lines 114 and 116, the microprocessor 102 transmits control signals to the fans 122 and 124 to control their rotation speeds. A relation between the temperature and the speed of the fan, which is indicated by a curve shown in FIG. 2, is stored in the microprocessor 102.
FIG. 2 depicts a relationship between the temperature and the rotation speed of the fan. For example, when the temperature detected by the thermal sensor 104 is less than the temperature T0, the fan will remain at a lower rotation speed R0. R0 represents the rotation speed of the fan when the system is initiated. When the temperature detected by the thermal sensor 104 ramps upwards to Ta, the microprocessor 102 increases the speeds of the fans 122 and 124 to Ra to improve the heat dissipation effect. Thereafter, as the temperature detected by the thermal sensor 104 ramps upwards to Tb, the microprocessor 102 continues to increase the speeds of the fans 122 and 124 to Rb. Thus, while the temperature detected by the thermal sensor 104 is between T0 and Tm, the microprocessor 102 adjusts the speeds of the fans 122 and 124 depending on the relationship of inner temperature and the fan speed. In addition, when the detected temperature exceeds Tm, the fan rotation speed will no longer increase, i.e. Rm, representing the highest rotation speeds of the fans 122 and 124. As a result, the working temperature of the electronic device cannot exceed Tm, the design temperature.
FIG. 3 depicts a flowchart of operating the conventional heat dissipation system. First, in Step 202, the thermal sensor detects the temperature T. In Step 204, the temperature T is transmitted to the microprocessor 102. In Step 206, the microprocessor 102 determines whether the temperature T is greater than T0, which represents a value pre-stored in the microprocessor 102. As the temperature T is less than T0, in Step 208, the microprocessor 102 will maintain the fan speed at R0. As the temperature T is greater than T0, in Step 210, the microprocessor 102 determines whether the temperature T is less than Tm, which represents another value pre-stored in the microprocessor 102. Accordingly, when the temperature T is above Tm, in Step 212, the microprocessor will maintain the fan speed at Rm. When the temperature T is between T0 and Tm, the microprocessor 102 determines whether the temperature T changes, as shown in Step 214. If no, in Step 216, the microprocessor 102 will still maintain the fan at the current speed. If yes, in Step 218, the microprocessor 102 chooses one corresponding speed from the relation table between the temperature value and the fan speed, and transmits the control signals to the fans 122 and 124 through the signal lines 114 and 116 to further adjust the fan speeds improving heat dissipation effect.
The environment in which the electronic device is used may be altered. When the electronic device is operated in an atmospheric pressure less than 1 bar, the air density is lower, and therefore the conventional heat dissipation system will face the challenge. When the atmospheric pressure is less than 1 bar, the fan generates less airflow at the same speed compared with the fan operating in a higher atmospheric pressure. As a result, even if the rotation speed keeps the same, the conventional heat dissipation system shown in FIG. 1 cannot effectively dissipate heat. When the fan generates less airflow due to lower air density, the airflow can take away much less heat, thus resulting in ineffective heat dissipation. If the temperature detected by the thermal sensor 104 is unchanged, the microprocessor 102 is unlikely to increase the speeds of the fans 122 and 124. As the heat accumulated inside the device, the electronic device may malfunction at any time due to abnormal temperature or aging components.